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Thread: Improving shifts via the ECM

  1. #1
    Forum tyhee Site Admin GMPX's Avatar
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    Default Improving shifts via the ECM

    Over the last couple of months there has been some talk in THIS thread regarding some new findings and tables for the 6 speed auto's.
    Common complaints are changed shift feel when running without a MAF, shift hanging issues with boosted engines (there's probably more to add).
    Although you can go in and change the shift pressures and desired shift times on the T43, the problem is it's own calculations are torque based. It does a lot of it's own 'thinking' based on the torque figure the ECM is reporting to it. The result of this torque figure being out usually results in the issues mentioned above.
    So how does the ECM measure engine torque? Well, it doesn't, it's calculated, and unless you change the tables used in the calculations the torque figure broadcast to the TCM is not going to be correct. Now we aren't talking to the nearest lb-ft here, but in testing we saw a drop of almost 40 lb-ft in the maximum reported torque just by going MAF-less. Ever notice how a MAF-less car doesn't shift as nice?

    So, the fix for this is not in the TCM, it's the ECM, we need to get the ECM to broadcast a more accurate torque figure of the engine for the TCM to work with. When that occurs, everything just falls in to place.

    Of course nothing is easy, there is two different torque models in use from 2006 to current.

    First the early style...



    And now the later style:




    They are very similar, but not quite the same so we gave them different table numbers.

    The calculation is along the lines of how the Virtual VE works, it takes a bunch of numbers from various tables, adds, multiplies several times over to end up with a final figure. We decided not to attempt to show these as a virtual VE table simply because there is too many variables used to be able to present it as one 3D map. However, in testing it was found there was really only one table that needed modifying to get satisfactory results. The images above show the table I mean, it's the engine Airflow contribution to the final torque figure.

    I will quote from the table descriptions....
    "Modifying coefficient values should be done with caution. Sometimes small changes in the table may cause big changes in the final calculated values. It is recommended that you change the values by only 5% at a time and then test the results. The final torque value from the Torque Model tables can be logged in the scantool using the PID - GM.TRQENG_C "Engine Actual Steady State Torque".

    Note: Don't be too concerned about the shape or smoothness of this map as it is a coefficient table, they tend to look erratic. Applying smoothing to make it look 'nice' may have negative results."


    There is really only one way to verify your changes, monitor the reported torque value using the scantool PID GM.TRQENG_C "Engine Actual Steady State Torque".

    All these updates have been included from RC10 up.

    Please post up your results for others to use as a guide.

    Cheers,
    Ross
    Last edited by GMPX; March 11th, 2012 at 01:50 PM.


  2. #2
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    Are you able to post the formula the coefficients are used in for interest sake?

  3. #3
    Forum tyhee Site Admin GMPX's Avatar
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    You are assuming I know it


  4. #4
    Lifetime Member Tre-Cool's Avatar
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    Just checking but when you say modify by 5% i assume you mean multiply. As that is what i did.

  5. #5
    Forum tyhee Site Admin GMPX's Avatar
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    No, enter in the change value (5) then press the % button, not the mutliply button. I hate to think what numbers you've ended up with by 'multiplying' by 5.


  6. #6
    Lifetime Member Tre-Cool's Avatar
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    sorry, i meant multiple by 5 percent. so make the numbers higher not lower.

    i started out with 15% on mine, it's definetly a bit better. unfortunatly im on the other side of the country again so i cant go through my logs but from the quick glanse i had at the v2 while cruising the reported eng tq numbers were definetly higher.

    just bare in mind im running 60lb injectors with 70psi fuel pressure & max'd out injector tables.

    LS3-HTV2300-60psi-fuel pressure_0032.tun6L80e-3500stall-3_0028.tun

  7. #7
    Lifetime Member Rhino79's Avatar
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    Ahh I see Tre, your os has base shift times, mine does not. Mine is based soley on tq reference.

  8. #8
    Lifetime Member Rhino79's Avatar
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    Currently Im at 15% and .3 on shift times below 2000 rpm and blending down to .15 shift times by 4000 rpm. Tight shift times at part throttle will cause a lazy shift. I tried .2 with negative results. .3 shifts quicker than it did with .2 shift times and shift feel was improved as well.

  9. #9
    Member scottcmb's Avatar
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    How do you work out which gearbox ""style"" you have? to know which table to use..........my vehicle is a 2008 HSV GTS LS3 with a T43

  10. #10
    Forum tyhee Site Admin GMPX's Avatar
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    You don't have to figure it out, the tables simply changed between years are are not shown if not in there, i.e, you won't see the same table set in a 2007 as you will a 2010.


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